1. Field of the Invention
The present invention relates to an accurate synchronization device. It applies in particular to the making of accurate measurements or accurate, or even ultra-accurate synchronization of information distributed from a transmitter to mutually remote receivers, for example for operating complex electromagnetic and/or optical rigs.
2. Discussion of the Background
Temporal information being distributed to geographically scattered receivers, the term accuracy is understood to mean a dispersion in arrival time of the order of 10 picoseconds and the term ultra-accuracy to mean a dispersion in arrival time of the order of a picosecond. It is therefore necessary to ascertain the distances between the transmitter and the receivers with an accuracy of the order of a centimetre for the accurate class and a millimetre for the ultra-accurate class.
The present-day electronic systems for clock distribution generally have a passband of the order of a gigahertz, thus allowing them to achieve resolutions of the order of a nanosecond.
To achieve the class of accuracy of the order of a few tens of picoseconds, that is to say a factor 100 with respect to the aforesaid passband, these systems require calibration and compensation functions of a complexity such that the ultra-accurate class is not conceivable, the ultra-accurate class being that of a picosecond, i.e. a factor 1000. Examples of implementation of such systems are found for example in laser amplification rigs.
To calibrate these electronic systems, it is necessary to employ means for measurements having around ten times better accuracy, that is say of the order of a picosecond, and hence inaccessible.
Finally, to operate these systems with an accuracy of the order of some 10 picoseconds, it is necessary to employ an extremely stable and unperturbed electromagnetic and thermal environment, thus rendering their use intricate in the presence of high-energy pulse-like waves.
The purpose of the invention is to allow the distributing of temporal information to geographically scattered receivers with an extremely low time dispersion. To this end, the subject of the invention is a device for synchronizing signals transmitted from a transmitter to receivers, characterized in that it comprises at least, at the level of the transmitter, means for generating a synchronization signal having a recurrence period substantially equal to the minimum resolution of the journey time between the transmitter and a receiver and, at the level of each receiver, means for delaying the synchronization signal and a synchronization loop comprising, downstream of the delay means, a semi-reflecting plate such that a part of the signal makes at least one outward/return trip between the receiver and the transmitter, and comprising correlation means and means for slaving the delay means dependent on the correlation, a signal received by a receiver being synchronized when the correlation function of two successive recurrences of the synchronization signal passing through the semi-reflecting plate is a maximum.
The main advantages of the invention are, in particular, that it makes it possible to achieve ultra-accurate synchronization of signals, that it allows the distributing of temporal information to a large number of receivers situated at very different distances from the transmitter, these distances possibly being large, that it is rather insensitive to the electromagnetic and thermal disturbances of the environment and that it makes it possible intrinsically to monitor the proper working of the synchronization and to correct any drifting in respect of each receiver.